The bolt from the blue came early on at the Olympic test event at the London Velodrome in February, on the first evening's racing, when Jess Varnish and Victoria Pendleton stepped up for the final of the women's team sprint. They had qualified second fastest to the Australian duo of Kaarle McCulloch and Anna Meares, which was as expected: the world champions had earlier set the world record, living up to their status as favourites, the established duo who owned the two-lap event.

That all changed in the space of a little over 30 seconds as Varnish set a personal best for the opening standing-start lap, breaking the 18.8sec barrier for the first time, and delivering Pendleton at such high speed that she was able to set a personal best as well, enabling the pair to smash the world record and push the Australians into a surprise second place.

In the buildup to London 2012 this August it could prove to be a key moment, as Varnish recognised a few days later, the point when the British duo – fourth in the 2010 world championships, runners up in 2011 – moved up a level. "We really showed them we were a force to be reckoned with," Varnish told the Observer. "I definitely think they weren't expecting it, because they had broken that world record in the first round. We weren't expecting it either. It showed them that we are there."

Most of the British sporting world now knows about Pendleton's fear of failure, her more-than-occasional doubts, and the fierce drive that has made the 2008 Olympic sprint champion the country's leading woman track racer and – together with Sir Chris Hoy – one of the leaders of the track cycling squad. But Varnish is the new girl on the block, progressing steadily since being thrown into action at the World Cup in Manchester a couple of months after the GB team's triumphant return from Beijing, laden with gold medals.

Varnish is the product of a cycling family from Bromsgrove, brought to the sport by her father Jim, the first cyclist to win a grand slam of national junior, under-21, senior and world titles at cycle speedway, and a master's sprint champion. She is one of a number of talented young women to emerge from the Halesowen cycling track in the west Midlands, of whom another is Helen Scott, who is likely to race the London Olympics as a paralympic tandem pilot.

The specific choice to specialise in the opening lap of the team sprint was made a couple of years ago. "It wasn't a hard decision. I wanted to be in the London Games in 2012, Vicky is very strong in the sprint and keirin, so starter was where I saw my place to be," Varnish said. Being "woman one" requires total specialisation to acquire the power needed to make the fastest start possible; since turning senior Varnish has increased her peak power output by a third, and she can now squat more than twice her bodyweight. "She has the highest peak power and torque output of any female in the whole team," says the sprint head coach, Iain Dyer.

Varnish's progression has been linear. In February 2011 she went through the 19sec barrier for the standing lap for the first time, a moment which the GB sprint coach, Jan Van Eijden, described as "a massive step physically and mentally". "That was a big step, I was the first British woman to break 19sec, but it wasn't enough. I keep thinking, 'I want to get another 0.2, another 0.2. I know what I can do in every training session, I push myself beyond my limits, see the numbers and everything going in the right direction, so I know I can do it."

There are other factors, such as the technique of getting away from the electronic gate as the start gun fires, as Dyer explains. "We decided after the worlds last year to do every start in every starts session [using] the gate, with electronic countdown, just like race day, in a bid to improve 'time in gate' before the get away." As a result, Varnish has now done more than 500 starts: no wonder she has made the discipline her own.

Together with Pendleton – whose poster hung on her wall at home in Bromsgrove when she was a teenager – she now forms a closeknit unit. The pair room together and, Varnish explained before the Olympic test event: "We get on really well. Before competition we are chilled out, we end up doing random stuff like pampering, face masks or watching Downton Abbey."

Intense training for the starting lap means that Varnish has no time to study the tactical niceties of the other sprint events, the match and keirin, which she rides at major championships as an add-on to the team event, but she is improving steadily there too, and fifth place in the sprint in the London World Cup suggests that by Rio in 2016 she could be a contender in that area too.

The world championships, which start on Wednesday in Melbourne, open with Varnish and Pendleton taking on the Australians Meares and McCulloch, who will be out for revenge in front of their home crowd in an event Meares has described as "a full dress rehearsal – physical, mental, emotional" for this summer's Olympics in London. But a partisan crowd will not affect Varnish. "To be honest, when I get up there for the start in the race for the lap I don't hear anything. It's weird, I just hear myself saying, 'Right, one thumping great effort.'"

And thus far, those "thumping great efforts" are paying rich dividends.